Increase in storage capacities has been progressing in storage apparatuses using storage media including magnetic disks, magneto-optical disks, and optical disks. In order to increase the storage capacities of the storage apparatuses, a technology called Redundant Arrays of Inexpensive Disks (RAID) to use multiple storage media to compose a storage apparatus is in widespread use.
Readout and writing of user data by using a cache memory is generally performed in such a storage apparatus in order to reduce the processing time needed for data access from a higher-level apparatus (for example, a host computer). A semiconductor memory, such as a dynamic random access memory (DRAM) or a static random access memory (SRAM), is normally used as the cache memory.
Upon reception of a request to read out user data from the host computer, the storage apparatus searches the cache memory for the user data to acquire the user data corresponding to the readout request and notifies the host computer of cache data that is acquired. If no user data is acquired from the cache memory, the storage apparatus acquires the user data stored in a storage device, such as a hard disk drive (HDD), and writes the acquired user data in the cache memory.
Upon reception of a request to write user data, the storage apparatus notifies the host computer that a writing process is completed at the time when the user data is stored in the cache memory. Then, the storage apparatus stores the user data stored in the cache memory in a disk.
Since a volatile semiconductor memory is used as the cache memory described above, the user data in the cache memory is erased with no supply of power to the cache memory. Accordingly, at the time of power failure, some storage apparatuses perform a backup process to save all the data in the cache memory in a non-volatile memory by using power for emergency.
However, with the technology in related art mentioned above, it takes a long time to perform the backup process. In this case, there is a problem in that the saving of the data stored in the cache memory in the non-volatile memory is not completed within a time period in which the power for emergency is capable of being supplied and, therefore, the data that is not saved is lost. Japanese Laid-open Patent Publication Nos. 6-309234 and 9-330277 are examples of related art